The present invention relates to wireless communication systems, and more particularly, to a method of reporting signal quality measurements from a wireless communications mobile terminal.
The present invention is particularly applicable to mobile terminals that employ improved demodulation/decoding algorithms to improve the performance perceived by the end-user. An example of such a mobile terminal would be a mobile terminal employing a multi-pass demodulation algorithm wherein class 1a bits that had been attained from a channel decoder are used to improve the quality of class 2 bits that are uncoded by performing an improved demodulation with the knowledge of the decoded class 1a bits. It is expected that such a multi-pass demodulation algorithm would result in improved performance as perceived by the user, compared with a mobile terminal that does not employ such an algorithm provided the carrier-to-interference ratios seen by the mobile terminals are similar.
A mobile terminal is typically required to record and report measurements of quantities such as the bit error rate and frame error rate perceived by the mobile terminal. These reported measurements are used by the wireless communications system to adjust its transmit power and to change the carrier to interference ratio. However, these values are dependent upon the demodulation/decoding algorithm used. Thus, an improved demodulation/decoding algorithm, such as a multi-pass demodulation approach, will result in improved, i.e., xe2x80x9cbetter,xe2x80x9d error measurements. When these better error measurements are reported to the wireless communications system, the system may respond by lowering power, etc., resulting in an increased error rates at the mobile terminal. Thus, an improved demodulation/decoding algorithm may act to extend the acceptable performance range, but the system may respond by using up the extra margin provided, resulting in no net increase in performance as perceived by the user. In such a situation, it is clear that the performance advantage perceived by the user through the use of the enhanced demodulation/decoding algorithm could be lost, and the benefit of implementing the improved algorithms is lost to the equipment manufacturer.
Thus, in order to preserve the performance advantage associated with improved demodulation/decoding algorithms, a new method of reporting signal quality measurements from a wireless communications mobile terminal method is needed.
The present invention helps preserve the performance improvements offered by enhanced demodulation algorithms so that such improvements may be perceived by the user. In preferred embodiments, mobile terminals operating according to the present invention demodulate incoming signals according to two different demodulation algorithms. The first algorithm is the primary algorithm used by the mobile terminal to prepare the signals for higher protocol level processing. For ease of reference, this algorithm is called the enhanced algorithm. The second algorithm is a secondary algorithm used primarily to determine error rates to be reported back to the base station. For ease of reference, this algorithm is called the basic, or conventional, algorithm. As will be apparent from the discussion below, the basic algorithm should be good enough to meet the demodulation performance specifications on the operation of the mobile terminal as set forth in the appropriate standard. The enhanced algorithm provides improved performance as compared to the basic algorithm, which implies that under similar signal to impairment conditions, the enhanced algorithm is expected to generate fewer errors than the basic algorithm for the same input signals.
Like the prior art, a mobile terminal operating according to the present invention reports signal quality measurements to the wireless communications system. However, the reported signal quality measurements are not those resulting directly from the use of the enhanced algorithm. The mobile terminal instead calculates the required measurements based on the demodulation using the basic algorithm and reports these values to the wireless communications system, rather than those based on the enhanced algorithm. In alternate embodiments, the mobile terminal does not actually demodulate according to the basic algorithm, but instead maps the results from the enhanced algorithm to what the expected results would be with the basic algorithm. In either case, the signal quality measurements reported to the wireless communications system are conceptually those of the basic algorithm, not the enhanced algorithm. As such, the wireless communications system should respond as if the mobile terminal is using the basic algorithm, thereby allowing the mobile terminal to retain its performance advantage gained by using the enhanced algorithm.